Influenza virus infection continues to be associated with substantial morbidity and mortality, and varied effects on human immune responses. Interferon production is stimulated but lymphocyte transformation responses are depressed. The specific aims of the proposed research are to determine (1) whether depressed transformation responses are due to macrophage-mediated suppression or macrophage dysfunction; (2) whether infected cells elicit a different spectrum of response than the infectious virus; and (4) in order to accomplish these aims, to identify the population(s) of human mononuclear leukocytes expressing viral antigens. (This work is a continuation of studies instituted under a Young Investigator Research Grant, AI 15547). Suppression of lymphobyte transformation by cells or soluble mediators will be tested by coculturing of control and virus-exposed cells, by addition to control cultures of supernatant culture fluids from virus-exposed cells, and by use of inhibitors of prostaglandin and hydrogen peroxide synthesis. Populations will be identified and sorted into infected and uninfected populations using flow cytometry and indirect immunofluorescent labelling with goat anti-influenza heteroantisera and mouse monoclonal anti-influenza antibodies. Monoclonal antibodies to leukocyte markers will be used to identify leukocyte subsets. Cells expressing viral antigens will be compared for function (such as support of transformation responses, stimulation of interferon production, stimulation of an autologous mixed leukocyte reaction) with non-infected cells. Understanding the mechanisms of the virus-induced effects on human immune function may aid in development of improved preventive or therapeutic regimens, and perhaps in the development of diagnostic assays for viral infection.